diagnosing maples and dogwood anthracnose

I live in Kitsap and my 50-year old maple is dying — what should I do?

Also, my Dogwood trees seem to be infected with anthracnose. Can you give me some information about this disease?

To get some information about your maple, you can consult with a Master Gardener at a WSU Kitsap County Extension Diagnostic Clinic.

Regarding dogwood anthracnose (Discula destructiva), it is a shame that so many of these beautiful trees are infected. You may be somewhat reassured to know that although the disease often causes tree death in the northeastern U.S., here in the Pacific Northwest, many trees survive. Douglas Justice, Curator of Collections at University of British Columbia Botanical Garden, discusses this on the UBC discussion forum.
Excerpt:
“Weather is probably the deciding factor in infection. A cool, wet period seems to be most conducive to infection, and such factors probably have to coincide with a specific time of tissue susceptibility. In other words, the conditions have to be “just right” for the disease to take off and become established. However, it is well documented that stress predisposes plants to disease susceptibility. Stressors for Cornus nuttallii (Pacific dogwood) would include compacted soil, poor drainage, full exposure with overly dry soil (C. nuttallii is adapted to a summer drought regime, but let’s be reasonable!) and wet soil in summer (e.g., irrigated soil — see previous comment).

Nearly all the local anthracnose-affected dogwoods recovered, including the wild natives and the even some of the more severely affected C. florida (eastern dogwood). Anthracnose has visited us subsequently, but mostly only on C. florida and urban C. nuttallii. This suggests that the there isn’t much anyone can do to prevent the disease from occurring and that as along as trees aren’t overly stressed, they will eventually recover. ”

A U.S. Forest Service article entitled How to Identify and Control Dogwood Anthracnose includes images which may help you to determine if your tree has anthracnose.

Master Garden Products.com provides a short article about dogwood anthracnose that contains a What to Do list.

University of Maryland College Home and Garden Information Center’s Integrated Pest Management Series HP #12 offers information about dogwood diseases and pests, including anthracnose.

Oregon State University Extension’s Online Guide to Plant Disease Control describes cultural controls for anthracnose. There is also an extensive list of chemical controls, which you may choose to ignore after reading Douglas Justice’s comments from the UBC discussion forum mentioned earlier:
“The application of fungicides is probably a waste of money and also likely counter-productive, particularly with a systemic such a benomyl, which will kill most of the good fungi, but probably not the target pathogen. Common fungal pathogens frequently develop resistance to this fungicide.”

greenscale color chart

I need a reference that lists the greenscale color of leaves (or plants).

It would be helpful to have more information about what you are trying to do. There are charts which show different shades of green in leaves as evidence of nitrogen levels, but these are mainly used in agricultural settings, such as rice cultivation.

If you are looking for charts used in horticulture, one tool for answering questions about plant colors is the Colour Chart put out by the Royal Horticultural Society. This is a set of numbered cards, in every imaginable color, that you can hold up to a flower or leaf in order to determine the standardized color. There is an extensive set of colors in the green scale. The problem with the RHS color chart is that it is expensive. If you are able to visit the Miller Library, we have a copy of this color chart that you are able to use in the library.

The Azalea Society of America has a page of information on color systems which includes the RHS Colour Chart, the Universal Color Language, Munsell, and others.

pests and diseases affecting laurel shrubs

I have two Portuguese laurel shrubs. One has large
reddish-purple leaf spots and the leaves on part of the shrub have
dropped. It looks like the fungus is spreading to part of the other
shrub. Do you have any suggestions? I have raked up as much of the
dropped leaves as I can. Would Daconil be safe for Portuguese laurels?
I also have Bonide multi-purpose fungicide (contains
chlorothalonil), but wanted to see if you thought it would be safe for
laurels. Thank you for any suggestions you may have.

While I cannot diagnose the problem remotely, I will offer several
possibilities of what may be causing the leaf spots on your Prunus
lusitanica (Portuguese laurel). The causes might be bacterial, fungal, or
environmental. According to Oregon State University’s Plant Disease database, English laurel (and other types of laurel) can suffer from leaf spots and shothole. (Search plant list under the letter P, for Prunus laurocerasus.) Excerpt:

Shothole symptoms are commonly observed on Prunus sp. and can be caused
by a variety of factors. The bacterium Pseudomonas syringae pv. syringae
and several fungi including Cercospora sp., Blumeriella sp., and
Wilsonomyces carpophilum (Coryneum blight) can cause leaf spots and
shothole on cherry laurel (English laurel, Otto Luyken, or ‘Zabeliana’).
Copper spray injury and boron toxicity can also cause leaf spotting and
shothole. When symptoms are advanced, it is not possible to identify the
cause specifically.

Cherry laurels (English laurel, Otto Luyken, or ‘Zabeliana’), P.
laurocerasus and sometimes other Prunus sp. including cherry and plum,
commonly show shothole symptoms resulting from cultural or environmental
stress. Research has failed to identify what specific stress is
responsible. Both container- and field-grown laurel can develop symptoms.

Symptoms: Necrotic leaf spots with circular to irregular margins.
Bacterial spots are brown surrounded by a reddish border with a yellow
halo. Abscission layers develop around necrotic leaf spots causing the
injured tissue to drop away, leaving holes and tattered areas in the leaf
(as if someone fired a shotgun at the leaf-thus the name shothole). After
tissues drop, most often it is difficult to determine specifically what
caused the initial injury. Observations of early symptom development,
signs, and symptoms on other areas of the plant may help make an accurate
diagnosis. Note the holes in the leaves.

Cultural control: No management practices have been shown to help reduce
physiological shothole. For disease-induced shothole, try the following
cultural practices.

Avoid overhead irrigation.

Remove and destroy fallen leaves.

Do not plant near other flowering or fruiting Prunus sp.

If the problem is physiological shothole, this is an environmental
disorder which cannot be controlled with chemicals, and infected parts of
the plant should be removed and destroyed.

Your description does not sound like bacterial blight, which in laurels
usually affects only the leaves, but this link, from University of
California, Davis’s Integrated Pest Management site, may help you see if
the symptoms match your plant.

Prunus lusitanica can also suffer from Phytophthora, which may be seen in affected leaves as reddish or purplish discoloration.

It would be best to find out for certain what is causing the problem
before attempting to treat it. I suggest bringing samples of the affected
leaves to one of the Master Gardener Clinics in our area.

I cannot recommend using pesticides such as Daconil or Bonide (which both
contain chlorothalonil), as I do not have a pesticide handler’s license.
Also, the information linked here, from Northwest Coalition for
Alternatives to Pesticides, indicates that there are many more concerns
(human health, environmental) about chlorothalonil than simply whether it
will harm the Portuguese laurel. If you do choose to use pesticides, you
must follow the directions to the letter. Another reason to find out the
specific cause of the leaf spot and leaf loss is that it is against the
law to use a pesticide on a pest or problem for which it was not
intended.

An alternative approach would be to prune the plants severely to
rejuvenate them. Portuguese laurel is a good candidate for this type of
renovation. Here is more information on how to do this type of pruning. Scroll down to the section on renovating evergreen shrubs. Excerpt, from the Royal Horticultural Society:

Aucuba, Buxus, Choisya, Euonymus, Ilex x altaclerensis, Ilex aquifolium,
Prunus laurocerasus, Prunus lusitanica, Taxus, and Viburnum tinus all
tolerate severe pruning. Many evergreens are best renovated over several
years, removing one-third to half of shoots to ground level, and reducing
all other shoots by one-third in the first year. Over the next couple of
years remove half of the older shoots to ground level.

on feeding plants vs. feeding the soil

I have a Viburnum x bodnantense, or what looks a lot
like one, and it is blooming already, although this year’s leaves have not
yet fallen off completely. Would the plant benefit from feeding? I have a
Miracle-Gro hose-dispenser and bottled feed which is sprayed at 30:1
dilution. Would this help the plant, which may be weakened by early
blooming? Would a later feeding help? I am afraid I’ll miss the
late December blooms this year. Is that true?

It is possible you have Viburnum x bodnantense. The cultivars ‘Dawn’ and
‘Charles Lamont’ bloom from late fall through early spring. Thus, the
blooms you are seeing are normal, not early, and they should continue
through the winter.
Here is a link to a local growing guide from Rainyside Gardeners.

I think that feeding your Viburnum with a synthetic chemical fertilizer
like Miracle-Gro would not be a good idea. Miracle-Gro will supply more
nitrogen than your Viburnum wants, and you might actually encourage leafy
growth at the expense of flowers. All your plant really needs is mulching
with good organic compost and occasional feeds of alfalfa, fish
fertilizer, or manure.

Local garden writer Ann Lovejoy describes how to fertilize trees and
shrubs in spring and fall in her book The Handbook of Northwest Gardening
(Sasquatch Books, 2004):

“Spring feeds are generally fast-acting, offering rapidly growing plants the nitrogen they need… A feeding mulch of compost can be fortified
with fast-acting alfalfa, which will release more nitrogen if used in
combination with composted manures. Alfalfa comes in meal or pellets…

“In fall, most plants stop producing fresh top growth… Fall is a good
time to feed roots, which continue to stretch and grow underground
despite low temperatures. Adding whole fish meal to your compost feeding
mulch will fortify growing roots with phosphorus…

“In my own garden I rarely feed plants directly, preferring to feed the
soil.”

You may find the following comments about Miracle-Gro of interest. I hope this helps, and I hope your Viburnum keeps on flowering!

Sciadopitys verticillata culture and growing habit

My neighbor wants to give us a prized Sciadopitys, 5-6′ high.
In transplanting this cultivar now in Skagit County, what would you
recommend? How tall do these get in the Pacific Northwest?

Sciadopitys verticillata is listed in Great Plant Picks, a website of
plants recommended for our area. Here is what they have to say about this tree:

Outstanding Qualities:

The thick, dark green needles of this unusual evergreen conifer are held
like the ribs of an umbrella around its stems, giving it a unique
appearance. It is very slow-growing and columnar in shape, which makes it
suitable for small gardens. Japanese umbrella pine (or parasol pine)
creates an eye-catching accent in the landscape. Despite its common name,
this is not a true pine (genus Pinus). Like the dawn redwood, Sciadopitys
was once widespread, even growing in Europe, where it is seen in the
fossil record. Due to climate changes and competition, its native range
was reduced to a few towns in central Honshu, in japan. However, it has
been grown around monasteries in Japan for centuries. This species is the
only one in the genus.

Culture:

Japanese umbrella pine grows well in full sun or part shade. It prefers
acidic soil that is well-drained (sandy is ideal) with some organic
matter. In very hot or windy sites, it may sustain damage to its thick
needles.

Growing Habit:

Japanese umbrella pine is an evergreen, coniferous tree. Its habit is
columnar to pyramidal, growing 6 to 7 feet high and 3 feet wide in ten
years. While it reaches 120 feet in the mountains of Japan, in
cultivation it is seldom taller than 30 feet, with a spread of about 10
feet.

Hardiness:

USDA zones 6 to 8

As for transplanting, University of Wisconsin’s Master Gardener manual
says to transplant balled and burlapped or container-grown plants, and
plant in rich, moist, acid soil in a sunny, open spot. Wind protection is
essential, and you should avoid hot spots with intense afternoon sun. It
is slow-growing, and drought tolerant once established.

knotweed control methods

I’m having difficulty removing knotweed from my garden. Can you give me advice on how to eradicate it?

I’m sorry to hear you are struggling with knotweed. Manual methods include
cutting, mowing, pulling, digging, or covering. Dig surface roots in
loose soil. Check frequently for new shoots and dig them up as soon as
you notice them. Cut stems close to the ground every two weeks throughout
the growing season. After cutting completely, you could instead decide
to cover the area of the knotweed patch and the immediate area around it
with black plastic or other impermeable material. This is a long-term
process, and it may take several years to eradicate the Polygonum. Here are some helpful links on knotweed:

Invasive Knotweeds from the King County Noxious Weed Control Program

Knotweed Biology and Control from the King County Noxious Weed Control Program

Controlling Knotweed in the Pacific Northwest (a large file!)

Japanese Knotweed from the PCA Alien Plant Working Group

on overwintering miniature tea roses

Do I need to take my miniature tea roses indoors for the winter?

Your message doesn’t mention where you live, so I don’t know how cold
your winters are. Bringing your roses into the house can be problematic,
because we tend to keep our homes too warm for the plant, which wants to
go dormant in winter. A cold but sheltered spot may be a better choice.
If you live in the Pacific Northwest, you can keep your roses outdoors
year-round. Christine Allen’s Roses for the Pacific Northwest (Steller
Press, 1999) says that miniature roses are extremely hardy, hardier than
many larger roses. They can survive winter in an unprotected pot unless
the soil freezes all the way through.

The following information from New Mexico State University Extension offers similar advice. Excerpt:

“The miniature rose is often hardier than the common hybrid tea rose, so
it will survive but not bloom through the winter in most parts of New
Mexico. It requires a cool, dormant period and will do poorly if brought
indoors where it will stay warm. I have also noticed that if it is
indoors during the winter, it is often attacked and even killed by spider
mites. Other insects also become a problem when plants are indoors.

“You have several options. One is to leave it in its pot and keep it
outside in a protected location. Plants in pots are more subject to
freezing during the winter because the soil in the pot can freeze
completely and drop to a lower temperature than soil in the ground unless
the pot is kept in a protected location. Plants in the ground may have
the soil freeze around the base of the plant, but the roots are often not
frozen. A sunny location that allows daily warming and nightly freezing
of the soil in the pot is not good. You will also need to make sure that
the soil in the pot does not dry completely during the winter. Roses need
some moisture in the soil around their roots even in the winter. Soil in
flower pots dries more quickly than in the ground.

“Another option is to plant the rose in the soil where the soil
temperature will remain more moderate and the soil will dry slowly. It is
late in the season for this, but it can be done. Don’t let it dry after
planting, and by applying a layer of organic mulch (bark, straw, etc.)
around the base of the plant, you can help maintain moderate temperatures
and prevent sudden temperature changes in the root zone.

“Finally, you can keep the rose in a protected, cool location, allowing it
to become dormant for several months, then prune it and bring it indoors
to begin blooming early in the spring. This allows it to have its winter
rest, but you can enjoy its flowering earlier than if it stayed outside.
Replanting in a large pot may be helpful to allow more root growth. A
miniature rose is called miniature not for the size of the plant but for
the size of the flowers. Some miniature roses can become fairly large
plants and need a large root zone to support growth and flowering. That
is why planting outdoors may be the best choice in the long run, but
repotting it allows a potentially useful compromise.”

Fall planting and transplanting of shrubs

I have red osier dogwood, buttonbush, elderberry, and willow
shrubs that I want to transplant. They are going to be transplanted near
a pond to strengthen the riparian buffer, and I wanted to know if it is
okay to plant them now. It’s late October but it has been very warm, 70’s
and 80’s, and not too cold at night yet. What are the optimal
transplanting conditions for these plants and will they take if I plant
them in the next week or so?

Are these mature plants, or nursery starts? Is it both hot and dry where
you are? Fall is usually a good time to plant and transplant here in the
Pacific Northwest, but we have ample fall rainfall. If it has been dry in
Poughkeepsie, you might want to wait. However, I looked at the forecast
for the next several days in your area, and it seems to be in the 40’s and
50’s, which should be fine.

Any relatively young plant should not present a problem when
transplanting. Below are general guidelines for planting/transplanting:

Fall Planting of Trees and Shrubs from Iowa State University

Excerpt (keep in mind this is from the mid-West):

“If plants from a nursery can be planted in the fall, what about moving
or transplanting established trees and shrubs from one locale to another?
As you might suspect, severing the roots of a plant (up to 95 percent in
some cases), hauling it out of the ground, and moving it to a completely
new site is a stressful operation, regardless of the season. Still,
transplanting can be successfully carried out if it is restricted to
those plants with a proven track record of surviving such a move in the
fall.

“Why is it that some plants can be planted at almost any time of the year
while others are saddled with much narrower windows of opportunity?
Reasons for these differences are a subject for debate, but the commonly
held belief is that plants with shallow, fibrous roots can usually be
planted with greater ease than those with fewer, larger roots. Prime
examples of difficult-to-plant trees are magnolia and tulip tree; both
have thick, fleshy roots. Other slow-to-establish species that are better
planted in spring include fir, birch, American hornbeam, American
yellowwood, ginkgo, larch, sweetgum, hophornbeam, oak, willow, bald
cypress, and hemlock.

“Notable tree species that can be successfully planted in the fall include
maple, buckeye or horsechestnut, alder, catalpa, hackberry, hawthorn,
ash, honeylocust, Kentucky coffeetree, crabapple, Amur corktree, spruce,
pine, sycamore, linden, and elm. Most deciduous shrubs are easily planted
in fall; however, broad-leaved evergreens like rhododendron and
narrow-leaved evergreens like yew prefer to be planted in the spring.

“Fall planting (mid-August to mid-October) takes advantage of favorable
soil temperatures and moisture conditions that promote the root growth
needed to sustain plants through their critical first year in the
landscape. Unfortunately, our midwestern climate is unpredictable, and
even the toughest plants may die if fall or early winter weather is
severe or erratic. But if healthy, vigorous plants are chosen, if proper
post-planting care is given, and if slow-to-establish species are
avoided, fall planting of trees and shrubs can be as successful as spring
planting.”

Cornell University Cooperative Extension has an online manual on planting
and care for trees and shrubs which includes a general recommendation of
late summer to fall for planting woody plants in New York State, as well
as a short list of species which should not be planted in the fall (it
mentions Cornus, but not specifically red osier dogwood). The main reason
not to plant too late in the fall would have to do with early frosts
causing the plants to heave out of the ground.

on overwintering dahlias

I have some beautiful red dahlias in two flower boxes on my front
porch. Two questions: I noticed some of the leaves at the bottom
of the plants are turning yellow and dropping although the plants
are still blossoming. What to do? Also, do I need to remove them
from the soil for the winter here?

To answer your second question first, you don’t have to dig up your
dahlias unless you prefer to do so. Here is what local gardening expert
Marianne Binetti says on this subject in her Seattle P-I
column:

“Laid-back gardeners should just leave their dahlia tubers in the ground.
Cut back the top growth after the first hard frost and then cover the
dahlia bed with a waterproof oilcloth tablecloth or tarp. Secure with
rocks or bark mulch. This keeps the tubers dry and in the spring you can
remove the covering and see what comes up. For dahlias worked into a
mixed bed, you can pile sword fern leaves on top and weigh these down
with a rock.

“It is the wet more than the cold that kills dahlia tubers.

“If you really need to dig and store dahlias, place them in open paper
bags, never plastic, and let them dry in a covered area for a few days
before storing.”

As for the yellowed leaves, it is hard to diagnose the problem via
e-mail. There is a chance that you could safely just keep removing and
disposing of the yellowed leaves. However, there are problems like
leafhoppers (an insect which feeds on the leaves and causes them to
become speckled, then turn dry and drop off), or viral diseases which can
cause yellow spotting or mottling of the leaves. I looked at The
Gardener’s Guide to Growing Dahlias by Gareth Rowlands (Timber Press,
1999), and found descriptions of leaves which have turned yellow due to a
number of causes, including chlorosis (the leaves are unable to produce
enough chlorophyll, and turn yellow if there us still carotin present, or
white in only xanthophyll remains). When a mature dahlia turns yellow, it
may be due to a nutrient imbalance (such as lack of magnesium or iron).
Without having the plants diagnosed, it is impossible to recommend a
remedy, so you may want to bring samples to a Master Gardener Clinic.

on overwintering container-potted gardenias

I have three small gardenias that I planted in
containers this summer. They have done wonderfully but I am
not sure what to do with them for the winter. I live in
Seattle, WA and am not sure if i should bring them inside?
Please advise me on the best way to take care of them. I can
also plant them but don’t think this is the right time to
plant?

I don’t know which species of Gardenia you are growing, but
according to the book Hot Plants for Cool Climates by Susan
Roth and Dennis Schrader (Houghton Mifflin, 2000), Gardenia
augusta (also called Gardenia jasminoides) may be
overwintered in a conservatory or as a houseplant, but you
will need to make sure it gets enough light, and is kept
cool, particularly at night. If you grow it indoors, it will
also require high humidity.

Missouri Botanical Garden advises the following:

“Plants appreciate significant humidity year-round. In the
St. Louis area, plants should be grown in pots or containers
in conservatories or warm rooms. Plants may be taken outside
in summer, but should be brought indoors in late summer/early
fall for overwintering. As an indoor plant, grow this
gardenia in bright light with moderate room temperatures.
Water moderately, but do not allow soils to dry out. Prune as
needed after flowering to shape. Fertilize as needed from
March to August. In St. Louis, this low growing plant could
be sited outside in the ground in a protected location with
an organic root mulch, however winter survival would be a
serious concern. Gardenias need lots of attention and are
generally considered to be difficult plants to grow well.”

We are considerably warmer in winter than St. Louis, and
there are a few Gardenia cultivars which are said to
withstand colder temperatures, such as ‘Klehm’s Hardy’ (to 0
degrees F), ‘Chuck Hayes’ (to zone 6b), and ‘August Moon’
(about 0 degrees). The book Palms Won’t Grow Here and Other
Myths by David Francko (Timber Press, 2003) mentions these
cultivars, and adds the following:

“Gardenias require extremely well-drained, highly organic
soils. This species does best in partial shade and definitely
out of winter sun and wind. (It) can be grown as a container
plant but does not do well as a houseplant. Plant it near an
entry way to your home or whatever part of your garden you
happen to gravitate toward most.”

Seattle gardening expert Ciscoe Morris also says that keeping
the Gardenia indoors is problematic, because our homes are
usually far too hot and dry in the winter months to keep this
plant happy. It is liable to get spider mites inside, and he
suggests taking a shower with your plants to keep the mites
off the leaves, and to give them a good dose of humidity.
Since you have three plants, you could experiment by bringing
one indoors and keeping it in the best possible conditions
(no excessive heat, good light, sufficient humidity), and
then place or plant the others in the garden in a sheltered
spot (away from wind and intense sunlight).